17. October 1996
In this lab we will be utilizing the Friedel Crafts process of acetylation of ferrocene. Ferrocene is an atom of iron bounded by two aromatic rings. We will use some reagents that will cause the ferrocene to add either one acetyl group to an aromatic ring or add two acetyl groups to each of the aromatic rings. In order to determine how well this process had worked we employed: IR spectra analysis, column chromatography, and a little TLC. This experiment is relevant in today's highly industrialized world. By utilizing many of the techniques we employ in this lab, a company can synthesize new types of materials or composites that could revolutionize an industry.
When we react the ferrocene with phosphoric acid and acetic anhydride, we obtain many disparate products. Not only do we get acetylferrocene, but we also get diacetylferrocene, some unreacted ferrocene reactant, and acetic acid as well. We will use thin layer chromatography (TLC), column chromatography (CG), and IR spectra analysis in order to determine the what proportions of each of these compounds will be present in the final product.
Both TLC and CG are excellent methods of measuring the presence of a given substance. Both methods turn around a compounds polarity. As one recalls, polarity is a measure of the electronegativity of a compound determined by their placement in the periodic chart. Specifically, in this lab we are talking about the difference in polarity between the atoms of oxygen and carbon. Ferrocene is relatively low to none in polarity. Acetylferrocene, because of the carbonyl functional group, is more polar than the ferrocene. Moreover, diacetylferrocene, because of the 2:1 ratio of the carbonyl groups over the acetylferrocene, is the most polar of the lot.
As stated above, both TLC and CG take advantage of polarity. Both methods have an extremely polar stationary phase; specifically, silica or alumina gel is used. Through this polar stationary phase, a mobile liquid phase is passed. Now, one can think of a polar stationary phase as a bully that waits in the high school halls for his hooligan friends. His hooligan friends, hooley's as I like to call them, always stay back to talk him; the rest of the normal student body simply keep walking and pass him. The idea here is: like- stays-with- like. Analogously, those compounds which are most similar to the stationary substrate will stay behind to "hang out". In this case, the more polar the compound is, then the more it will stay behind as the rest of the product moves forward in its liquid mobile phase. TLC works by capillary action, where the mobile phase is drawn up the TLC plate and across a polar TLC plate. CG, on the other hand, works by having gravity pull the liquid mobile phase down a polar laden column. The joyous wonder of TLC and CG, then, is that they are thus able to separate each constituent contained in the product.
Methods & Procedure
The procedure of for this lab may be found in the pre-lab note for this experiment contained in the appendix. I will only remark on the important features of the procedure. The amount of start material for this lab was ca. 10 g. The calculation for this may also be found in the pre-lab I first added acetic anhydride to ferrocene (FC) and then warmed to add in the H3PO4 catalyst. I observed a reddish-violet color to this mix of reactants. I then did a TLC and noted that the majority of the sample was not the original ferrocene start material. Please see the pre-lab for reproductions of the TLC plates used in this lab. Also see table 1.2 for Rf values.
As one can see, this crude's Rf is half that of the start material. This indicates that a reaction has definitely occurred. Next we performed an extraction on this sample with Methylene Chloride (MeCl) and Sodium Hydroxide (OH-). Please see the pre-lab for a...